1. Field of the Invention
This invention relates to an apparatus for propelling pipes such as sewer pipes, conduit pipes and the like in the ground between a start shaft and a destination shaft in order to install the pipes in the ground and, more particularly, to an intermediate pipe-jacking apparatus removably disposed between the pipes to be propelled in order to compensate for a thrust of a basic pipe-propelling apparatus installed in the start shaft.
2. Description of the Prior Art
An intermediate pipe-jacking apparatus is adapted to propel a group of pipes in front of the intermediate pipe-jacking apparatus with a reaction borne by another group of pipes at the rear of the intermediate pipe-jacking apparatus. Such intermediate pipe-jacking apparatus is composed of hydraulic jacks and a support for supporting the hydraulic jacks. After the completion of propulsion of the pipes, the intermediate pipe-jacking apparatus is removed. Then, a space between the pipes resulting from the removal of the intermediate pipe-jacking apparatus is eliminated by propelling the rear group of pipes relative to the front group of pipes by the use of a basic pipe-propelling apparatus.
A conventional intermediate pipe-jacking apparatus as disclosed in Japanese Utility Model Public Disclosure (KOKAI) No. 63-156292 permits a plurality of hydraulic jacks to respectively shift from the position between the end faces of the adjacent front and rear pipes to the inside of the pipes of the support installed in the pipes. After the completion of propulsion of the pipes, the conventional pipe-jacking apparatus.
However, each of the conventional apparatuses including the apparatus disclosed in the above Public Disclosure occupies essentially the entire cross section of the pipe, in which the apparatus is installed, so that laser beams used for controlling the propulsion are hindered. Also, in pipes having a bore large enough to permit the operator to enter therein, it is advantageous if the operator can move through the intermediate pipe-jacking apparatus for the purpose of the removal, or the maintenance and inspection of the intermediate pipe-jacking apparatus or the adjacent pipes. However, the conventional intermediate pipe-jacking apparatus does not permit to the operator to carry out the above actions due to the structure as noted above.
Further, since the space between the pipes needs to be eliminated by the operation of the basic pipe-propelling apparatus after the removal of the intermediate pipe-jacking apparatus, the time needed to remove the basic pipe-propelling apparatus after an arrival of leading pipe at the destination shaft varies depending upon the time taken for the removal of the intermediate pipe-jacking apparatus. Accordingly, while the time taken to remove the intermediate pipe-jacking apparatus should desirably be shortened, the conventional intermediate pipe-jacking apparatus is of a type, having a plurality of hydraulic devices which are individually shifted inward of the pipe, so as not to satisfy this need at least with respect to controllability.